In recent years, such an optical image measurement technique has received attention that forms an image representing the surface morphology or internal morphology of a measured object by using a light beam from a laser light source or the like. Unlike an X-ray CT device, this optical image measurement technique does not have invasiveness to a human body, and therefore, is expected to be applied particularly in the medical field.
Patent Document 1 discloses an optical image measurement device having such a configuration that: a measuring arm scans an object by using a rotary deflection mirror (a Galvano mirror); a reference mirror is disposed to a reference arm; at the outlet thereof, such an interferometer is used that the intensity of a light appearing due to interference of light fluxes from the measuring arm and the reference arm is analyzed by a spectrometer; and the reference arm is provided with a device that gradually changes the light flux phase of the reference light in non-continuous values.
The optical image measurement device disclosed in Patent Document 1 uses a method of the so-called “Fourier Domain OCT (Optical Coherence Tomography).” That is to say, the morphology in the depth direction (the z-direction) of a measured object is imaged by radiating a low-coherence light beam to the measured object, acquiring the spectrum intensity distribution of the reflected light, and subjecting the acquired distribution to Fourier transform.
Furthermore, the optical image measurement device described in Patent Document 1 is provided with a Galvano mirror that scans with a light beam (a signal light) so as to be capable of forming an image of a desired measurement target region of a measured object. Because this optical image measurement device scans with the light beam only in one direction (the x-direction) orthogonal to the z-direction, a formed image is a two-dimensional tomographic image in the depth direction (the z-direction) along a scan direction of the light beam (the x-direction).
Patent Document 2 discloses a technique of scanning with a signal light in the horizontal direction and the vertical direction to thereby form a plurality of two-dimensional tomographic images in the horizontal direction and, based on the plurality of tomographic images, acquiring and imaging three-dimensional tomographic information of a measurement range. As a method for three-dimensional imaging, it is possible to employ, for example, a method of arranging and displaying a plurality of tomographic images in the vertical direction (referred to as stack data or the like), and a method of forming a three-dimensional image by subjecting a plurality of tomographic images to a rendering process.
Patent Document 3 discloses a configuration in which the optical image measurement device as described above is applied in the opthalmologic field. In the opthalmologic field, the optical image measurement device is specifically used as a fundus oculi observation device for observing the fundus oculi. In the fundus oculi, layers such as the retina and the choroidea exist. Moreover, in the retina, the internal limiting membrane, the nerve fiber layer, the ganglion cell layer, the inner plexiform layer, the inner nuclear layer, the outer plexiform layer, the outer nuclear layer, the external limiting membrane, the photoreceptor cell layer and the retinal pigment epithelium layer exist in order from the fundus oculi surface side in the depth direction. The fundus oculi observation device is used for acquiring tomographic images showing the morphologies of these layers. Moreover, it is possible to analyze the thickness of the layer based on the tomographic image. The result of the analysis of the layer thickness is displayed in a graph along the cross-sectional position, for example.
Patent Document 4 discloses an optical image measurement device that executes a measurement while changing the wavelength of a light radiated to a measured object. This optical image measurement device is called the Swept Source type or the like.    [Patent Document 1] Japanese Unexamined Patent Application Publication No. 11-325849    [Patent Document 2] Japanese Unexamined Patent Application Publication No. 2002-139421    [Patent Document 3] Japanese Unexamined Patent Application Publication No. 2003-543    [Patent Document 4] Japanese Unexamined Patent Application Publication No. 2007-24677